1. Field of the Disclosure
The present disclosure relates to Magnetic Resonance Imaging (MRI) methods that provide imaging with reference to time. More particularly, the present disclosure relates to improvements in scan time for MR imaging, in particularly accelerated 4D flow imaging.
2. Description of the Related Art
Medical imaging devices provide images of certain internal portions of a patient's body, and provides a vitally important tool in the detection and treatment of various medical conditions. Various types of medical imaging devices exist and often having respective advantages associated with performing imaging of different areas of the body to be viewed, such as ultrasonic diagnostic equipment, x-ray tomography equipment, magnetic resonance imaging equipment, and medical diagnostic equipment.
In general, magnetic resonance (MR) imaging equipment functions provide superior contrast images of soft tissues of a human body, as well as provide various types of diagnostic information. Therefore (MR) imaging equipment is a critical resource for diagnostic technology using medical images.
Image reconstruction in an MRI apparatus involves decoding of measured signals in order to identify and map spatial frequency components to spatial locations. While conventional Fourier reconstruction methods have been improved upon in recent years, constrained reconstruction methods use a priori information in order to compensate for a lack of high frequency data in a reconstruction process. Thus, the additional information to restore information beyond a measurement cutoff can be derived.
In addition, k-space refers to a matrix of spatial frequencies that has a mathematical relationship to an image (whose Fourier transform is the MR image), and in the case of digitized MRI signal data, virtually every point in k-space represents a spatial frequency and is used to add to signal intensity.
Moreover, Echo Planar Imaging (EPI) is a methodology that is used in part to obtain medical images. With regard to EPI, rather than measuring a single echo subsequent to transmitting a pulse, EPI permits the acquisition of many echoes. EPI is used to acquire more signals from an excitation pulse.
The use of EPI is seen as one possible way to reduce scan time because multiple k-space lines can be acquired for each phase, which is beneficial to Phase Contrast (PC) imaging in which flow encoding gradients are applied after each RF excitation.
However, conventionally, there have been some issues with EPI. While the acquisition time per slice with EPI can be on order of 100 ms/slice, there is a rather limited spatial resolution.
Recent advances in both hardware and software MR technologies have permitted EPI to be used for faster, higher temporal and spatial resolution flow imaging. However the importance of k-space trajectories used in EPI sequences increases when using EPI for faster, higher temporal images.
In general, a magnetic resonance (MR) imaging device includes imaging equipment that diagnoses internal structures of a human body using the energy—already converted to a signal—induced from resonance reactions obtained by applying a constant rate of frequency and energy to nuclei of atoms of a patient while a predetermined magnetic field is applied to the patient.
MR imaging extends beyond conventional 2D imagery, for example, 3D MRI, in which two dimensional slices are joined together so as to permit a 3-dimensional model, and dynamic imaging such as flow sensitive 4D MRI, which provides ECG synchronized flow sensitive 3DMRI. Flow sensitive 4D MRI data permits a useful quantification if items being directly measured, show as flow rates, and permits the use of pressure difference maps, pulse wave velocity, etc. Flow sensitive 4D MRI can permit analysis of blood flow through peripheral blood vessels, carotid artery, intracranial arteries, artificial valves, etc.
The scan time associated with dynamic imaging can be significantly long, on upwards of 30 minutes. Not only does this extended time increase costs of operation, but also discourages the use of such scanning as the accuracy and validity of such resulting data. Patients do not like and/or are sometimes able to be still for such a length of time, particularly when enclosed within a confined scanning area of the MRI apparatus.
Image reconstruction in an MRI apparatus involves decoding of measured signals in order to identify and map spatial frequency components to spatial locations. While conventional Fourier reconstruction methods have been improved upon in recent years, constrained reconstruction methods use a priori information in order to compensate for a lack of high frequency data in a reconstruction process. Thus, the additional information to restore information beyond a measurement cutoff can be derived.
In addition, k-space refers to a matrix of spatial frequencies that has a mathematical relationship to an image (whose Fourier transform is the MR image), and in the case of digitized MRI signal data, virtually every point in k-space represents a spatial frequency and is used to add to signal intensity.
Moreover, Echo Planar Imaging (EPI) is a methodology that is used in part to obtain medical images. With regard to EPI, rather than measuring a single echo subsequent to transmitting a pulse, EPI permits the acquisition of many echoes. EPI is used to acquire more signals from an excitation pulse.
The use of EPI is seen as one possible way to reduce scan time because multiple k-space lines can be acquired for each phase, which is beneficial to Phase Contrast (PC) imaging in which flow encoding gradients are applied after each RF excitation.
However, conventionally, there have been some issues with EPI. While the acquisition time per slice with EPI can be on order of 100 ms/slice, there is a rather limited spatial resolution.
Recent advances in both hardware and software MR technologies have permitted EPI to be used for faster, higher temporal and spatial resolution flow imaging. However, the importance of k-space trajectories used in EPI sequences increases when using EPI for faster, higher temporal images.
There is difficulty in providing high-resolution MRI of an object when there is motion is involved, for example, an MRI of organs such as the coronary arteries, lungs, etc. associated with both cardiac and respiratory motion. While there can be temporal triggering as the motion tends to be generally repetitive motion, the amount of scan time that can be needed to obtain an acceptable image can be excessive.
Moreover, heretofore it has not been feasible to obtain dynamic image with a 4D cine phase contrast as part of a clinical cardiac MRI protocol, as such cardiac MRI protocol includes evaluations of items such as function, anatomy, and scar imaging.
Accordingly, there is a long-felt need in the art to decrease the scan time of EPI methodologies when utilizing MR imaging in dynamic imaging, including but in no way limited to, for example, a 4D-PC flow imaging.